diff --git a/chrome/content/zotero-platform/mac/overlay.css b/chrome/content/zotero-platform/mac/overlay.css
index 9c5ff55c95..578332313f 100644
--- a/chrome/content/zotero-platform/mac/overlay.css
+++ b/chrome/content/zotero-platform/mac/overlay.css
@@ -25,7 +25,7 @@
 #zotero-context-splitter:not([state=collapsed])[orient=horizontal]
 {
 	-moz-appearance: none;
-	border-inline-start: 1px solid #bdbdbd;
+	border-inline-start: var(--material-panedivider);
 	margin-inline-end: -4px;
 	width: 5px !important;
 	min-width: 5px;
diff --git a/chrome/content/zotero-platform/win/overlay.css b/chrome/content/zotero-platform/win/overlay.css
index e08ab05002..cbe3f0ed0f 100644
--- a/chrome/content/zotero-platform/win/overlay.css
+++ b/chrome/content/zotero-platform/win/overlay.css
@@ -29,7 +29,7 @@
 #zotero-items-splitter:not([state=collapsed]):not([orient=vertical]),
 #zotero-tags-splitter:not([state=collapsed]),
 #zotero-context-splitter:not([state=collapsed]) {
-	border-inline-end: 1px solid var(--theme-border-color);
+	border-inline-end: var(--material-panedivider);
 	min-width: 0;
 	width: 3px;
 	margin-inline-start: -3px;
@@ -38,7 +38,7 @@
 #zotero-tags-splitter:not([state=collapsed]),
 #zotero-items-splitter:not([state=collapsed])[orient=vertical],
 #zotero-context-splitter-stacked:not([state=collapsed]) {
-	border-block-end: 1px solid var(--theme-border-color);
+	border-block-end: var(--material-panedivider);
 	min-height: 0;
 	height: 3px;
 	margin-block-start: -3px;